Technical Field
The present invention relates to a semiconductor device including a high-side driver circuit and a low-side driver circuit which drive a totem pole-connected high-side switching device and low-side switching device in a complementary manner.
Background Art
FIG. 11 schematically illustrates the configuration of a power converter including a totem pole-connected high-side switching device XM1 and low-side switching device XM2. This power converter functions as a DC/AC converter which generates AC power for a load RL by alternately outputting a DC voltage HV and a ground voltage to the load RL via the switching devices XM1 and XM2, which are switched ON and OFF in a complementary manner.
A semiconductor device 1 which includes a high-side driver circuit 11 and a low-side driver circuit 12 and switches the switching devices XM1 and XM2 ON and OFF in a complementary manner is implemented as an intelligent power module (IPM), for example. This semiconductor device 1 further includes an interface circuit 13 which generates a high-side drive signal and a low-side drive signal in a complementary manner in accordance with a control signal IN input from a controller 2 (an external device). The high-side driver circuit 11 switches the high-side switching device XM1 ON and OFF in accordance with the high-side drive signal, and the low-side driver circuit 12 switches the low-side switching device XM2 ON and OFF in accordance with the low-side drive signal. The high-side drive signal generated by the interface circuit 13 is input to the high-side driver circuit 11 via a level shifter circuit 14.
Here, the low-side driver circuit 12 and the interface circuit 13 receive and operate on a prescribed supply voltage VCC, with a ground voltage GND as a reference voltage. The high-side driver circuit 11 uses an intermediate voltage VS at a series connection node between the switching devices XM1 and XM2 as a reference voltage and receives and operates on a boosted supply voltage VB generated by boosting (bootstrapping) the supply voltage VCC in a bootstrap circuit constituted by a bootstrap diode Dbs and a bootstrap capacitor Cbs.
The bootstrap circuit charges the bootstrap capacitor Cbs with the supply voltage VCC when the low-side switching device XM2 is ON. When the low-side switching device XM2 switches OFF, the bootstrap circuit utilizes the increase in the intermediate voltage VS (the low-voltage side terminal voltage of the bootstrap capacitor Cbs) that occurs as the high-side switching device XM1 switches ON to thereby generate the boosted (bootstrapped) supply voltage VB.
Typically, in the semiconductor device 1 configured as described above, if the ON time of the high-side switching device XM1 is long, for example, decreases in the charge stored in the bootstrap capacitor Cbs become more pronounced, and it may not be possible to maintain the supply voltage VB required to drive the high-side driver circuit 11.
To solve this problem, Patent Document 1, for example, discloses supplying current to the bootstrap capacitor Cbs from a floating power supply FV (which uses a high-voltage side voltage as a reference voltage) when the low-side switching device XM2 is OFF (see FIG. 1 in Patent Document 1). However, the configuration disclosed in Patent Document 1 requires preparing the floating power supply FV and creates problems such as increases in cost and how to configure the floating power supply FV itself in the first place.
Furthermore, Patent Document 2 discloses charging the bootstrap capacitor Cbs directly from the high-voltage DC voltage HV via a resistor R1 when the low-side switching device XM2 is OFF (see FIG. 1 in Patent Document 2). However, the configuration disclosed in Patent Document 2 creates a problem where when the high-side switching device XM1 is ON, the DC voltage HV and the intermediate voltage VS take substantially the same voltage, and the resistor R1 becomes a load for the supply voltage VB and discharges the charge stored in the bootstrap capacitor Cbs.
Moreover, when the low-side switching device XM2 is ON, the intermediate voltage VS and the ground voltage GND take substantially the same voltage, thereby causing the charging current of the bootstrap capacitor Cbs to increase. In addition, a clamp current flowing through a Zener diode for regulating the charge voltage of the bootstrap capacitor Cbs also increases. As a result, the power consumption of the bootstrap circuit increases, and it becomes more difficult to miniaturize the semiconductor device 1.
As illustrated in FIG. 12, to address this, Patent Document 3 discloses charging a first-stage capacitor C1 with the supply voltage VCC via switching devices Qn1 and Qn2 and then charging a second-stage capacitor C2 with the charge voltage of the capacitor C1 via switching devices Qp1 and Qp2. In the configuration disclosed in Patent Document 3, under the control of a control circuit 15, the switching devices Qn1 and Qn2 and the switching devices Qp1 and Qp2 are switched ON and OFF in a complementary manner independently of the ON/OFF operation of the switching devices XM1 and XM2, thereby generating the supply voltage VB as the charge voltage of the second-stage capacitor C2. Therefore, even when the OFF time of the low-side switching device XM2 is long, it is possible to maintain the supply voltage VB required to drive the high-side driver circuit 11.